content: /**
   * Copyright (c) 2017, Andy Janata
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without modification, are permitted
   * provided that the following conditions are met:
   *
   * * Redistributions of source code must retain the above copyright notice, this list of conditions
   *   and the following disclaimer.
   * * Redistributions in binary form must reproduce the above copyright notice, this list of
   *   conditions and the following disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
   * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
   * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
   * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
   * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package net.socialgamer.cah.metrics;
  
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  import java.util.Date;
  import java.util.UUID;
  import java.util.concurrent.atomic.AtomicLong;
  
  import net.socialgamer.cah.CahModule.ServerStarted;
  
  import org.apache.log4j.Logger;
  
  import com.google.inject.Inject;
  import com.google.inject.Provider;
  import com.google.inject.Singleton;
  
  
  /**
   * <p>A provider for server-wide unique IDs, which will not conflict with another server or if this
   * server restarts.</p>
   * <p>Unique IDs are composed of the following elements, separated by underscores:
   * <ul><li>server hostname (or a random UUID if the hostname cannot be determined)</li>
   * <li>the number of milliseconds since the UNIX epoch at the time the server was started</li>
   * <li>a long interger that strictly increases each time an ID is requested</li></ul></p>
   *
   * @author Andy Janata (ajanata@socialgamer.net)
   */
  @Singleton
  public class UniqueIds implements Provider<String> {
  
    private static final Logger LOG = Logger.getLogger(UniqueIds.class);
  
    private static final String hostname;
  
    private final AtomicLong counter = new AtomicLong(0);
    private final Date serverStarted;
  
    static {
      String hn;
      try {
        hn = InetAddress.getLocalHost().getHostName();
      } catch (final UnknownHostException e) {
        hn = UUID.randomUUID().toString();
        LOG.warn(String.format("Unable to determine hostname, using %s instead.", hn));
      }
      hostname = hn;
    }
  
    @Inject
    public UniqueIds(@ServerStarted final Date serverStarted) {
      this.serverStarted = serverStarted;
    }
  
    @Override
    public String get() {
      // hostname_started_seq
      return String.format("%s_%d_%d", hostname, serverStarted.getTime(), counter.getAndIncrement());
    }
  }
  